Adaptable spring force clamping apparatus and methods

ABSTRACT

Adaptable spring force clamping apparatus and methods are disclosed. In one embodiment, an apparatus includes at least one elongated member adapted to be positioned proximate to a surface of a work piece. The elongated member includes first and second end portions adapted to be secured to substantially prevent movement of the elongated member relative to the surface. A plurality of pressure applying devices are operatively attached to the elongated member, each pressure applying device including a contact member moveable relative to the elongated member and adapted to engage the surface of the work piece, and a resilient member operatively coupled to the contact member and to the elongated member.

GOVERNMENT LICENSE RIGHTS

This invention was made with Government support. The Government hascertain rights in this invention.

FIELD OF THE INVENTION

This invention relates generally to assembly tools, and, morespecifically, to clamping mechanisms.

BACKGROUND OF THE INVENTION

Equipment and vehicles, including aircraft, often utilize sheets or longsections of metal that need to be clamped together or to a frame duringassembly of the equipment. Assembly may include welding or other bondingprocesses. Typically clamps of various configurations are utilized tohold materials in place during welding, bonding or other assembly. Forexample, if welding is being utilized to bond segments of skin to eachother or the underlying framing, the skin segments typically are held inplace during that process.

Existing clamps often span the surface being clamped, being anchored attheir ends. For example, metal bars, shaped to conform to the section orsurface being worked on have been utilized as clamps, by being anchoredat their respective ends and held tightly against the surface beingworked on. It will be appreciated that clamping a bar at its ends acrossa work surface results in a differential amount of pressure beingapplied to the work surface across the span of the bar. This occursbecause the bar deflects somewhat with the application of clamping forcefrom the ends. Typically the clamped work piece is not held as securelyin the center of the span of the clamp bar as it is near the ends wherethe ends are anchored. In some circumstances, this differential clampingforce can result in insufficient clamping force being applied to thework piece, or differential stresses in the work piece after assembly.While larger clamping bars may be utilized to reduce deflections acrosstheir span when clamped against a work piece, increased size requiresincreased effort to manipulate and to use in jigs and assembly modules.

Therefore, an unmet need exists for adaptable clamps that provideimproved clamping of surfaces during manufacturing operations.

SUMMARY OF THE INVENTION

The present invention is directed to adaptable spring force clampingapparatus and methods. In one embodiment, an apparatus includes at leastone elongated member adapted to be positioned proximate to a surface ofa work piece. The elongated member includes at least one portion adaptedto be secured to substantially prevent movement of the elongated memberrelative to the surface. A plurality of pressure applying devices areoperatively attached to the elongated member and disposed therealong,each pressure applying device including a contact member moveablerelative to the elongated member and adapted to engage the surface ofthe work piece, and a resilient member operatively coupled to thecontact member and to the elongated member. The resilient member biasesthe contact member away from the elongated member to apply a clampingforce to the surface of the work piece. In alternate embodiments, twoelongated or spanning members with pressure applying devices may bemounted parallel to each other, or alternately, a single elongated orspanning member with a slot formed therein may provide access forwelding or other manufacturing work in the clamped area.

In accordance with still further aspects of the invention, the apparatusof the present invention may be curved or angled. The apparatus may alsobe two-dimensional, such as cruciform shaped. In accordance with anotheraspect of the invention a clamping apparatus in accordance with thepresent invention is included with an assembly manufacturing jig holdingthe work piece. In further aspects of the invention, a method isprovided for welding skin segments of an aircraft to adjoining sectionsor to underlying framing utilizing the clamping method of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings.

FIG. 1A is an isometric view of an angled clamp bar assembly inaccordance with an embodiment of the present invention;

FIG. 1B is an end elevational view of a single clamp bar of the angledclamp bar assembly of FIG. 1A;

FIG. 1C is a side elevational view of the angled clamp bar assembly ofFIG. 1A;

FIG. 1D is a partial top elevational view of the angled clamp barassembly of FIG. 1A;

FIG. 2 is an end cross-sectional view of the clamp bar assembly of FIG.1A in place on a work piece;

FIG. 3 is an isometric view of a straight clamp bar assembly inaccordance with an alternate embodiment of the present invention;

FIG. 4 is an isometric view of an assembly jig incorporating a cruciformclamp bar assembly in accordance with yet another embodiment of thepresent invention;

FIG. 5 is a flow chart of an exemplary assembly method in accordancewith yet another embodiment of the present invention;

FIG. 6 is an end elevational view of an offset clamp bar assembly inplace on a work piece;

FIG. 7 is an isometric view of the offset clamp bar assembly of FIG. 6in place on a work piece.

FIG. 8 is an isometric view of a cantilevered clamp bar assembly inplace on a work piece.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to adaptable spring forceclamping apparatus and methods. Many specific details of certainembodiments of the invention are set forth in the following descriptionand in FIGS. 1–8 to provide a thorough understanding of suchembodiments. One skilled in the art, however, will understand that thepresent invention may have additional embodiments, or that the presentinvention may be practiced without several of the details described inthe following description.

By way of background, in one embodiment, an apparatus includes a memberarranged to at least partially span a work piece with at least onepressure applying device attached to the member. The at least onepressure applying device may include a plurality of spring-loaded padsarranged to apply pressure to a work piece. Two spanning members withpressure applying devices may be mounted parallel to each other, or asingle spanning member with a slot suitably may provide access forwelding or other work in the clamped area.

Turning to FIG. 1A, an exemplary angled clamp bar assembly 20 inaccordance with an embodiment of the present invention is shown. Theassembly 20 includes two clamp bars 22 arranged in parallel with a slot24 between them. The clamp bars 22 in this exemplary embodiment aremetal bars with a single obtuse angle bend in the middle. The clamp bars22 may be any suitable material and cross-section that carriessufficient stress to apply a desired clamping force to a work piece. Thework piece (not shown) is spanned by the clamp bars 22 with the workpiece underneath or inside the angle of the clamp bars 22. In apresently preferred embodiment of the present invention, 1018 steelalloy bars 1¾″×1 ⅛″ are utilized for the clamp bars 22.

The clamp bars 22 may be parallel and may be coupled together by twosteel angle stock hold-downs 38 fastened to the ends of the clamp bars22 by fasteners 39. In this embodiment, the hold-downs 38 are suitably⅜″ steel 90° angle stock with one limb of the angle stock fastened tothe ends of the clamp bars 22. The hold-downs 38 thus hold the clampbars 22 in position parallel to each other but separated by the width ofthe slot 24. The other limb of the hold-down 38 has an opening 40through which a bolt or other fastener may be inserted to attach theassembly 20 over a work piece, as described more fully below. In thisembodiment, there are two hold-downs 38, one at each end of the clampbars 22. The hold-downs 38 thus hold the clamp bars 22 in position withrespect to each other, and also suitably attach the entire assembly 20in position over the work piece. It will be appreciated that the clampbars 22 may be curved, straight, segmented, or any other desired shape.It will also be appreciated that the two clamp bars 22 and thehold-downs 38 may suitably be manufactured from one piece, or adifferent combination of pieces forming the assembly 20.

In this example embodiment, the clamp bars 22 have a plurality ofspring-loaded pads 32 along their lengths that may apply force againstthe work piece. The pads 32 extend outwardly from a bottom side of theassembly 20. Both clamp bars 22 have a plurality of spring-loaded pads32 along their lengths. The spring-loaded pads 32 are mounted on keepers30 which project through the clamp bars 22. The keepers 30 have springs36 or other pressure-applying devices (see FIG. 1B) mounted incounter-bored holes 27 on the bottom of the clamp bars 22, as describedin more detail with reference to FIG. 1B and FIG. 2 below. The slot 24between the clamp bars 22 allows access to the work piece between theclamp bars 22. Thus the assembly 20 allows clamping pressure to beapplied by the pads 32 to the work piece while allowing access to thework piece between the clamp bars 22 through the slot 24.

While clamping pressure is applied on both sides of the slot 24 usingthe clamp bar assembly 20, a variety of manufacturing operations may beperformed on the work piece, including, for example, welding, heatbonding, adhesive application or other bonding methods, milling,sanding, routing, riveting, drilling, or virtually any other desiredmanufacting operation. Welding processes suitably may includetraditional welding or friction stir welding. A tool (such as one usedfor the bonding process) may be inserted through the slot 24 to accessthe work piece while the work piece is clamped on both sides of the slot24. In this embodiment, clamping force is applied in a parallel with theslot 24 between the clamp bars 22.

FIG. 1B is an end elevational view of an single exemplary clamp bar 22such as those used in the angled clamp bar assembly 20 of FIG. 1A. Thespring-loaded pad 32 is attached to a keeper 30 which projects through ahole 26 through the clamp bar 22. The pad 32 is on the bottom of theclamp bar 22 (i.e.on the side towards the work piece when the assembly20 is attached across the work piece). The pad 32 is spring-loadedagainst the work piece by the spring 36 installed in the counter-boredhole 27 in the bottom of the clamp bar 22. The keeper 30 retains the pad32 and the spring 36 in place on the clamp bar 22, as described ingreater detail in connection with FIG. 2 below. The spring 36 suitablyapplies a predetermined clamping pressure against the work piece.

It will be appreciated that various embodiments of the instant inventionmay include one or more clamp bars 22. A clamp bar assembly having asingle clamp bar may suitably be used where, for example, clamping isonly desired on one side of a joint or connection. Similarly, multipleclamp bars 22 in different configurations suitably provide clampingpressure over a wide range of configurations and surfaces. A pair ofclamp bars 22 arranged close to each other with a slot 24 in betweenadvantageously allow clamping pressure to be simultaneously applied toboth sides of a joint line positioned under the slot 24.

FIG. 1C is a side elevational view of the exemplary angled clamp-barassembly 20 shown in FIG. 1A. As is shown in this side view, each clampbar 22 has two straight limbs 28 and a single central angle bend 29. Atboth ends 25 of the clamp bar 22 are the 90° angle stock forming thehold-downs 38. The hold-downs 38, at each end 25 of the clamp bars 22,are fastened to the clamp bars 22 by fasteners 39.

In this example configuration the clamp bar assembly 20 has eighteenspring-loaded pads 32 with eighteen keepers 30, nine of each on eachclamp bar 22. Furthermore, in this embodiment, four pads 32 with fourkeepers 30 are on each limb 28 of the clamp bars 22 and one pad 32 andone keeper 30 is located at the bend 29 of the angled clamp bar 22. Thepads 32 apply pressure to the work piece approximately perpendicular tothe clamp bar 22 when the clamp bar 22 is held in place by thehold-downs 38 at each end. The pad 32 and keeper 30 at the bend 29 applypressure against the work piece approximately parallel to a line thatbisects the angle of the bend 29 of the clamp bar 22.

FIG. 1D is a partial top elevational view of an end of the angled clampbar assembly 20 of FIG. 1A. Again, as viewed from the top, the two clampbars 22 are separated by the slot 24. In this view of one end of theclamp bar assembly 20, two spring loaded pads 32 and their respectivekeepers 30 are on portions of the limb shown of the clamp bars 22 (thebalance is cut off in this abbreviated top view of the end of theassembly 20). Attached to the ends 25 of the clamp bars 22 is thehold-down 38. The hold-down 38 is attached by fasteners 39 to the clampbars 22. The two clamp bars 22 are held in position parallel to andseparated from each other by the hold-down 38. The hold-down 38 has anopening 40, in this example in the form of a notch, that allows theassembly 20 to be bolted or attached to a frame or support (not shown)with the clamp bars 22 spanning a work piece.

FIG. 2 is a cross sectional view of the clamp bar assembly 20 of FIGS.1A through 1D in place on a work piece 4. The cross section in FIG. 2 isthrough the two clamp bars 22 at a location in each clamp bar 22 havinga pad 32 and a keeper 30. Thus, the pad 32, keeper 30, and the spring 36spring-loading the pad 32 are also shown in cross section.

As further shown in FIG. 2, the work piece 4 in this example includesthe top of an I-beam frame 6 and two segments of skin (or panels) 8 tobe installed in place and joined on the frame 6. The skin segments 8preferably come together on top of the frame 6 at a joint 7 centeredbelow the slot 24 of the clamp bar assembly 20. As described above, theslot 24 in the clamp bar assembly 20 allows a bonding tool 10 to beutilized to form a bond of the skin segments 8 to each other and,depending upon the application, to the underlying frame 6 at the joint7.

In FIG. 2, the tool 10 may be a shouldered friction stir welding tool.Friction stir welding is a solid state joining process that is acombination of extruding and forging. A cylindrical shouldered tool witha profiled pin is rotated and slowly plunged into a joint line betweenpieces of material which are clamped together. Frictional heat isgenerated between the welding tool 10 and the work piece 4. The heatcauses the work piece 4 to soften without reaching the melting point andallows the tool to traverse the joint 7 line. As it does, plasticizedmaterial is transferred from the leading edge of the tool 10 to thetrailing edge of the tool 10 shoulder and pin. This leaves a solid phasebond along the work piece. While the clamp bar assembly 20 may beutilized to provide access to the joint 7 through the slot 24 forfriction stir welding, it suitably may be used for any other weldingprocess, bonding process, or manufacturing process. In operation, withthe clamp bar assembly 20 centered with the slot 24 over the joint 7,the spring-loaded pads 32 hold the skin segments 8 hard against theunderlying frame 6 on either side of the joint 7. The joint 7 can thenbe worked, welded, or bonded with the tool 10, using access through theslot 24 between the clamp bars 22. Access through the slot 24 spans thework piece, with parallel rows of clamping pads 32 on either side of thejoint 7.

It will be appreciated that the pads 32 used to clamp the skin segments8 may be attached with any suitable pressure applying device to theclamp bars 22 to provide a desired clamping pressure. In therepresentative clamp bar assembly 20 shown in FIG. 2, the pads 32suitably include a pad 33 backed by a backing disc 34. The backing disc34 is attached to a machine screw 35 which forms the keeper 30. Themachine screw 35 projects from the bottom surface 18 of the clamp bar 22to above the top surface 16 of the clamp bar 22 through a hole 26. Thehole 26 is counter-bored from the bottom 18 with a counter-bore 27providing space for a spring 36. The spring 36 applies clamping forcevia the pad 32 to the work piece 4. The counter-bore 27 may becounter-bored into the bottom 18 of each clamp bar 22 a suitabledistance so that when the clamp bars 22 are held in place near the workpiece 4, the springs 36 apply the desired amount of pressure to the workpiece 4 via the pad 32.

A slippery or cushioning pad 33 may be used to cushion or prevent thescratching of the work piece 4 by the spring-loaded pad 32. In apreferred embodiment, the pad 33 may be TEFLON®. The pad 33 may bemounted to its backing disc 34 utilizing flush-mounted fasteners (notshown), including, for example, counter-sunk machine screws threadedinto the metal backing disc 34. The pads 32 are suitably round, but maybe any desired shape. The backing disc 34 for the pad 33 may have a holeat its center tapered to accept the head of the flathead machine screw35. The machine screw 35 fits through the backing disc 34 forming asurface that is flush or flat, permitting the pad 33 to be installedover the backing disc 34 and the machine screw 35 forming a flatclamping surface for the spring-loaded pad 32. In a presently preferredembodiment, the machine screw 35 suitably may include a ¼-20×2½″flathead machine screw. The backing disc 34 suitably includes a 1/16″steel disc, and the pad 33 suitably includes a 1/16″ thick TEFLON® disc.The machine screw 35 forming the keeper 30 holding the pad 32 and spring36 in place projects through the hole 26 in the clamp bar 22. In thisexemplary embodiment, the hole 26 is suitably a ¼″ hole.

By way of example but not limitation, in one representative embodiment,the two clamp bars 22 suitably are separated from each other by the slot24 with a width of ¾″, and the counter-bore 27 providing space for thesprings may be 0.875″ in diameter and 0.75″ deep. Furthermore, in anexemplary embodiment, the clamp bars 22 themselves are suitably 1.75″tall and 1.125″ wide. It will be appreciated that any suitabledimensions for the slot 24, pads 32, keeper 30, and the clamp bars 22that provide access to the work piece and make provision for the keepers30 to be moveably linked to the clamp bars 32 and apply clampingpressure to the work piece 4 may be utilized.

In yet another aspect of the embodiment shown in FIGS. 1A through 2, themachine screw 35 forming the keeper 30 is held from falling out of theclamp bars 32 with two jammed nuts 31, threaded on the machine screw 35where the screw 35 projects through the top surface 16 of the clamp bar22. The jam nuts 31 are suitably installed at the very top of themachine screw 35, above the top surface 16 of the clamp bar 22. The jamnuts 31 have a larger outside diameter than the hole 26 through theclamp bar 22 and thus hold the machine screw 35 in place. This retainsthe spring 36 and the pad 32 in place on the clamp bar 22 when the clampbar is removed from the work piece 4. The spring 36 within thecounter-bore 27 applys force from the clamp bar 22 to the pad 32 againstthe work piece 4. The machine screw 35 included in the keeper 30 issuitably long enough to project through the clamp bar 22 and be held bythe jam nuts 31 while giving sufficient clearance for the pad 32 to bespring-loaded by the spring 36 away from bottom 18 of the clamp bar 22.

The spring (or pressure applying device) 36 suitably provides clampingpressure to the work piece 4. In a preferred embodiment, the springs 36may be Danley Die Springs # 9-1204-36. With the clamp bar assembly 20installed in place spanning the work piece 4, the die springs 36 cansuitably apply a force of approximately 228 lbs each against the workpiece 4. It will be appreciated that the springs 36 may be shimmed, orthe counter-bore 27 depths varied, to provide varying degrees ofclamping force where, for example, additional or varying clamping forceis desired, or to provide for equal clamping pressure across the entirespan of the clamp bars 22. This suitably may compensate for deflectionwhen the clamp bar assembly 20 is held against a work piece 4 with thespring-loaded pads 32 engaging and clamping the work piece 4.

The pressure applying devices 36 applying clamping pressure to the workpiece 4 via the pads 32 suitably may include any type of pressureapplying device other than springs 36, such as resilient materials,hydraulic pistons, pneumatic bladders, or any other suitable pressureapplying device. A resilient material may include, for example, a softplastic or rubber material. It will be appreciated that springs 36, evenwithout further shimming, provide relatively even pressure when severalspring-loaded pads 32 project from the clamp bars 22 spanning a workpiece 4. As the clamp bar assembly 20 is held against the work piece (orvice versa) 4 with the bars 22 spanning the work piece 4, the springs 36are placed in compression applying clamping force against the work piece4 on both sides of the joint 7 being worked on. It will be appreciatedthe jam nuts 31 keep the keeper 30 in place when the assembly 20 isremoved from the work piece 4.

Turning to FIG. 3, it will be appreciated that a clamp bar assembly 120in accordance with an embodiment of the present invention may befabricated using a single spanning or elongated member 122. In theexample embodiment shown in FIG. 3, the spanning member 122 has a slot124 formed through it lengthwise, for access to a work piece (notshown). The spanning member 122 suitably may be manufactured from asingle bar of steel with the slot 124 cut through the bar. The slot 124is cut through the bar along its length, but not all the way through tothe ends, leaving it as one piece. At the ends (or at one or morelocations, see FIG. 8 below), the spanning member 122 may be suitablybolted to a tower or attachment over a work piece (not shown) with theuse of fastening bolts 138. In this embodiment, the two clamp bars 22,and the two hold-downs 38 of FIG. 1A are combined into a single integralcomponent spanning member 122 of FIG. 3, with the cut slot 124longitudinally cut through the spanning member 122.

In the embodiment shown in FIG. 3, a straight clamp bar assembly 120 issuitably formed by the straight spanning member 122. As with otherconfigurations of the present invention, the spanning member 122suitably may be angled, segmented, or curved to conform to the surfaceof the work piece (not shown) being clamped. The embodiment shown inFIG. 3 is straight for use in clamping a flat work piece (not shown).

As in the angled clamp bar assembly 20 of FIGS. 1A–1D, the straightclamp bar assembly 120 of FIG. 3 includes two parallel rows ofspring-loaded pads 32 disposed on opposite sides of the slot 124. Theslot 124 suitably provides access to a joint or elongated work areaunderneath the assembly 120, when the assembly 120 is in place over awork piece. The assembly 120, through its pads 32, may suitably applypressure on two sides of a joint centered underneath the slot 124 in thespanning member 122 when the spanning member 122 is attached in place orheld against a work piece. The pads 32 may be held in place by keepers30 projecting through the spanning member 22 in the manner describedabove with reference to FIG. 2.

It will be appreciated that the clamp bar assembly 120 of the presentinvention may be held in place against a work piece, or the work piecemay be pushed against the assembly 120 by a jig, lift, or otherassembly. Put differently, clamping force can be applied by holding theassembly 120 against the work piece, or by holding the work pieceagainst the assembly 120.

FIG. 4 shows another exemplary embodiment of the present inventionincluding an assembly jig 210 for an aircraft segment. The assembly jig210 suitably includes a base 214 with a plurality of supports or cradles12 for holding the frame for a fuselage segment (not shown). Attached tothe base 214 are a plurality of towers 250 to which are attached a clampbar assembly 220 of the present invention. In this example embodiment,the clamp bar assembly 220 is approximately cruciform shaped. The clampbar assembly 220 includes four limbs 228 intersecting at 90° in a crossshape bridging over a work piece (not shown) when the work piece is heldin place on the cradles 12 of the jig 210. The clamp bar assembly 220thus has four pairs of rows of spring-loaded pads 232 held in place bykeepers 230. Each limb 228 of the cruciform shaped clamp bar assembly220 has a slot 224 centered in the limb 228 and extending longitudinallyalong the limb 228. Each slot 224 allows access to the work piece whenthe assembly 220 is in place on the jig 210 for welding, bonding, orother manufacturing work.

As further shown in FIG. 4, in this embodiment, three of the limbs ofthe cruciform shaped clamp bar assembly 220 are co-planar while a fourthlimb is bent at an angle away from the plane of the other limbs. Theclamp bar assembly 220 thus may apply clamping force along anintersecting pair of joints in the work piece, including across anangled three-dimensional surface of the work piece.

The clamp bar assembly 220 is held over the top of the cradles 12 byfasteners 248 to towers 250 attached to the base 214. Two of the limbsof the cruciform shaped clamp bar assembly 220 are held to the towers250 by angle bar hold-downs 238, while two other limbs of the assembly220 are held in place with fasteners 248 through the clamp bars 222. Itwill be appreciated that any suitable combination of attachments betweenthe clamp bar assembly 220 and the towers 250 holding the clamp barassembly 220 to the jig 210 may be utilized. It will also be appreciatedthat the clamp bar assembly 220 may be fixedly mounted (e.g. to a flooror other suitable support structure), and a work piece on moveablesupports or cradles 12 may be moved underneath or alongside the clampbar assembly 220 and pushed against the clamp bar assembly 220 with asuitable mechanism resulting in a clamping force being applied to thework piece. The assembly jig 210 of FIG. 4 may be configured with avariety of clamp bar assemblies 220 to quickly and efficiently allowmanufacturing operations, including bonding work such as welding orfriction stir welding, to be completed on complex shaped equipment andequipment sections. This may include bonding work traversing a varietyof contours, as well as multiple segments intersecting at differentangles as required for the assembly of the work piece.

Embodiments of the present invention may also suitably includes themethods of clamping work pieces, and working work pieces, in the mannerdescribed in connection with FIGS. 1–4 above. Embodiments of methods inaccordance with the present invention may permit uniform application ofclamping force across a work piece, and working the work piece alongside or between the clamping mechanism(s) of the present invention.

FIG. 5 illustrates an exemplary process 300 of performing amanufacturing process (e.g. friction stir welding) on a pair of skinsegments of a portion of an aircraft frame in accordance with yetanother embodiment of the present invention. The method 300 may begin ata block 310, in which a portion of a support frame is cradled. Cradlingthe support frame may include placing the frame within an assembly jig,such as the assembly jig described above in connection with FIG. 4. At ablock 320, at least one skin segment is positioned over the frame. Itwill be appreciated that, as in FIG. 2, at the block 320, two adjoiningskin segments may be butted together along the top of the support frame.

As further shown in FIG. 5, at a block 330, at least part of the portionof the frame and the at least one skin segment are bridged forming aspan from which clamping pressure can be applied. The span can be asingle span, permitting work to be done on the work piece on either sideof that span, or the span can include two parallel spans, permittingworking of the work piece in a slot between the spans such as shown anddescribed above in connection with FIG. 2. The span may completelybridge the work piece, may be along side the work piece as described inconnection with FIGS. 6 and 7 below, and may be cantilevered over theworkpiece as described in connection with FIG. 8 below. In embodimentswhere two parallel spans are utilized, at a block 340, the method 300may include defining a slot over a joint on the work piece to be worked.In this exemplary embodiment, the joint suitably includes two buttedskin segments over a frame member of an aircraft, positioned in themanner as described above in connection with FIG. 2.

With continued reference to FIG. 5, in this embodiment, at a block 350both sides of the joint are clamped. The slot or opening defined by thespans permits the work piece to be worked on between the clamped areas.At a block 360, a manufacturing operation may be performed on the workpiece (e.g. welding). Suitably, in one embodiment of the method 300, thetwo abutting skin segments positioned over the frame member of a portionof the frame of the aircraft may be friction stir welded by inserting atool through the slot in the span, while the skin segments on both sidesof the joint may be securely clamped in the manner described above usingapparatus in accordance with embodiments of the present invention. Thus,it will be appreciated that the method 300 may advantageously facilitatethe secure and rapid clamping and working of a work piece, even whenperforming a manufacturing operation on the work piece involves theapplication of substantial force, such as in friction stir welding.

Turning to FIG. 6, it will be appreciated that clamping force may beresiliently applied from along side a work piece 4. FIG. 6 is an endelevational view of an exemplary clamp assembly 400 with keepers 405that extend laterally over a work piece, transmitting clamping forcefrom clamp bars 422 along side the work piece 4. The work piece 4includes a frame member 6, and two covering skin sections 8, to bejoined together at a joint 7 over the frame member 6. A clamp bar 422 ispositioned on each side of the work piece 4. Attached to the clamp bars422 are keepers 430, mounted on supports 431 with fulcrums 433 attachedto the clamp bars 422. The keepers 430 form a lever arm projectingacross the fulcrums 433 out over the the work piece 4, in thisembodiment from two clamp bars, one on each side of the work piece 4.The keepers 430, in this exemplary embodiment, are resiliently biased bysprings 436 between their first ends 437 situated over the clamp bars422, and the clamp bars 422. The springs 436 thus bias the keepers' 430second ends 439, which project over the work piece 4, hard against thework piece 4, applying clamping force to the work piece 4. In thisembodiment, the fulcrums 433 are pivots linking the keepers 430 to thesupports 431, permitting force from the springs 436 applied to the firstends 437 of the keepers 430 to be transmitted to the work piece 4 by theopposite second ends 439 of the keepers 430.

The springs 436 are suitably held in place in position between the clampbars 422 and the first ends 437 of the keepers within counterbores 427and 428 in the clamp bars 422 and keepers 430, respectively. The ends ofthe springs 437 nest within the counterbores 427 and 428. In thisembodiment, the second ends 439 of the keepers 430, over the work piece4, have pads 432, that apply the clamping force to the work piece 4.

The clamp assembly 400 applies clamping force from both sides of thework piece 4. A distance or slot 424 between opposing second ends 439 ofthe keepers 430 projecting over the work piece 4 allows the work piece 4to be worked along the joint 7 without interference from the assembly400. The distance or slot 424 between the keepers 430 allows a workingtool 10 to be moved along the joint 7, between the pads 432 applyingclamping force.

As shown in FIG. 7, the clamp bars 422 of FIG. 6 may be of any suitableconfiguration positionable along side the work piece 4. FIG. 7 is anisometric view of the clamp bar assembly 400 of FIG. 6 in position overa work piece. The assembly 400 iincludes a plurality of keepers 430 thatproject over the work 4 from both sides. The keepers 430 apply resilientclamping force to the work piece 4 in the manner described with respectto FIG. 6. The clamp bars 422 are suitably elongated triangular trussesthat form a support for the keepers 430. Two clamp bars 422 arepositioned one on each side of the work piece 4, each with a pluralityof keepers 430 projecting over the work piece 4. The clamp bars 422suitably provide sufficient moment resistance when positioned along sidethe work piece 4 to compress the springs 436 resulting in clamping forcebeing applied to the work piece by the keepers 430, and their attachedpads 432.

It will be appreciated that a clamp assembly of the present inventionmay be positioned with respect to a work piece in a range ofconfigurations. In FIG. 8, an exemplary clamp assembly 500 iscantilevered over a work piece 4. As in FIG. 3, an elongated clamp bar522 has a longitudinal slot 524 cut through the bar 522. On each side ofthe slot 524 are a plurality of spring-loaded keepers 530 projectingthough the bar 522. The spring-loaded keepers retain springs (not shown)that apply clamping force biasing pads 532 against the work piece 4. Inthis embodiment the clamp bar 522 is attached to a base 502 at one end523, while the opposite end 525, with the slot 524 and the plurality ofspring loaded keepers 530 projects over the work piece. The base 502 isattached to a foundation surface 501 that also supports the work piece4. It will be appreciated that cantilevering the clamp bar 522 from abase 502 may allow the work piece 4 to be slid or moved in underneaththe clamp bar 522, without detaching the clamp bar 522 from the base502.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is not limited by the disclosure of the preferredembodiment. Instead, the invention should be determined entirely byreference to the claims that follow.

1. An apparatus for applying a clamping force against a surface of awork piece, the apparatus comprising: first and second substantiallystraight elongated members, the elongated members being approximatelyparallel and spaced apart to define an elongated slot therebetween, theelongated members being further adapted to be positioned proximate thesurface of the work piece and further adapted to be secured tosubstantially prevent movement of the elongated members relative to thesurface; and a plurality of pressure applying devices operativelyattached to the first and second substantially straight elongatedmembers and disposed therealong, each pressure applying device includinga contact member moveable relative to an associated one of the first andsecond elongated members and adapted to engage the surface of the workpiece, and a resilient member operatively coupled between the contactmember and to the associated one of the first and second elongatedmembers, the resilient member biasing the contact member away from theelongated member to apply a clamping force to the surface of the workpiece.
 2. The apparatus of claim 1 wherein at least one of the elongatedmembers includes a first end portion and a second end portion adapted tobe secured to substantially prevent movement of the elongated memberrelative to the surface.
 3. The apparatus of claim 1 wherein at leastone of the elongated members includes a first end portion and a secondend portion adapted to be secured to an adjacent structure so that theelongated member extends across the surface of the workpiece tosubstantially prevent movement of the elongated member relative to thesurface.
 4. The apparatus of claim 1 wherein the resilient memberincludes at least one of a spring and a resilient material.
 5. Theapparatus of claim 4 wherein the resilient material includes at leastone of a rubber and a compressible plastic.
 6. The apparatus of claim 1,wherein at least one pressure applying device applies at least one of ahydraulic pressure and a pneumatic pressure.
 7. The apparatus of claim1, wherein the at least one elongated member includes a substantiallystraight segment.
 8. The apparatus of claim 1, wherein the at least oneelongated member includes a curved segment.
 9. The apparatus of claim 1,wherein the elongated member includes a segment including an angle. 10.The apparatus of claim 1, wherein the contact member includes at leastone pad arranged to apply the clamping force against the surface. 11.The apparatus of claim 10, wherein the at least one pad includes aTEFLON® layer.
 12. The apparatus of claim 1, wherein the plurality ofpressure applying devices includes a plurality of resiliently loadedpads attached along a span of the elongated member over the surface andarranged to apply the clamping force to the surface at a plurality oflocations.
 13. The apparatus of claim 1, further comprising third andfourth substantially straight elongated members coupled to the first andsecond elongated members, respectively, the third and fourth elongatedmembers being approximately parallel and spaced apart to define a secondelongated slot therebetween, the third and fourth elongated membersbeing further adapted to be positioned proximate the surface of the workpiece, and further adapted to be secured to substantially preventmovement of the elongated members relative to the surface; and aplurality of second pressure applying devices operatively attached tothe third and fourth substantially straight elongated members anddisposed therealong, each second pressure applying device including asecond contact member moveable relative to an associated one of thethird and fourth elongated members and adapted to engage the surface ofthe work piece, and a second resilient member operatively coupledbetween the second contact member and to the associated one of the thirdand fourth elongated members, the second resilient member biasing thesecond contact member away from the elongated member to apply a secondclamping force to the surface of the work piece.
 14. The apparatus ofclaim 13, wherein the third and fourth elongated members are coupled tothe first and second elongated members to form an angular assembly. 15.The apparatus of claim 14, wherein the third and fourth elongatedmembers are coupled to the first and second elongated members to form acruciform shape.
 16. An apparatus for applying a clamping force againsta surface of a work piece, the apparatus comprising: an elongated memberadapted to be bridged across the surface of the work piece, theelongated member adapted to be secured to substantially prevent movementof the elongated member relative to the surface; the elongated memberdefining a slot with a first side and a second side, the elongatedmember including a first portion and a second portion on first side andthe second side of the slot, respectively; and a plurality of pressureapplying devices distributed along the first and second portions, eachpressure applying device being moveably coupled to a respective one ofthe first and second portions and including a contact member moveablerelative to the respective one of the first and second portions andadapted to engage the surface of the work piece, and a resilient memberoperatively coupled between the contact member and to the respective oneof the first and second portions, the resilient member biasing thecontact member away from the respective one of the first and secondportions to apply a clamping force to the surface of the work piece. 17.The apparatus of claim 16, wherein at least one of the pressure applyingdevices includes a spring.
 18. The apparatus of claim 16, wherein atleast one of the resilient members includes a resilient material. 19.The apparatus of claim 18 wherein the resilient material includes one ofrubber and compressible plastic.
 20. The apparatus of claim 16 whereinthe at least one of the resilient members applies the clamping forceutilizing one of hydraulic pressure and pneumatic pressure.
 21. Theapparatus of claim 16 wherein the first portion includes a firstsubstantially straight segment, and the second portion includes a secondsubstantially straight segment, and the first substantially straightsegment being positioned proximate and parallel to the secondsubstantially straight segment, and wherein the plurality ofpressure-applying devices are coupled to the first and secondsubstantially straight segments.
 22. The apparatus of claim 16 whereinthe elongated member includes a curved segment.
 23. The apparatus ofclaim 16 wherein the elongated member includes an angled segment. 24.The apparatus of claim 16 wherein the at least one of the contactmembers includes at least one pad arranged to distribute the clampingforce against the object.
 25. The apparatus of claim 16 wherein the atleast one pad includes a TEFLON® layer.
 26. The apparatus of claim 16,wherein the elongated member includes a first end portion and a secondend portion adapted to be secured to an adjacent structure tosubstantially prevent movement of the elongated member relative to thesurface.
 27. The apparatus of claim 16 wherein the slot includes aplurality of intersecting limbs.
 28. The apparatus of claim 26, whereinthe slot in plan view defines a cruciform shape.
 29. An apparatus forclamping a work piece during a manufacturing process, the apparatuscomprising: a first elongated member adapted to be positioned proximatea surface of the work piece, the first elongated member including atleast one portion adapted to be secured to substantially preventmovement of the first elongated member relative to the surface; a secondelongated member adapted to be positioned approximately parallel withand spaced apart from the first elongated member and forming anelongated slot therebetween, the second elongated member being adaptedto be secured to substantially prevent movement of the second elongatedmember relative to the surface; and a first plurality of pressureapplying devices operatively attached to the first elongated member asecond plurality of pressure applying devices operatively attached tothe second elongated member, each pressure applying device including acontact member moveable relative to an associated one of the elongatedmembers and adapted to engage the surface of the work piece, and aresilient member operatively coupled between the contact member and theassociated one of the elongated members the resilient member biasing thecontact member to apply a clamping force to the surface of the workpiece.
 30. The apparatus of claim 29 wherein the resilient memberincludes a spring.
 31. The apparatus of claim 30 wherein the resilientmember includes a resilient material.
 32. The apparatus of claim 30wherein the contact member is adapted to project across at least aportion of the surface of the work piece.
 33. An apparatus for clampinga skin to a frame during a manufacturing process, the apparatuscomprising: at least one cradle adapted to support the frame; at leastone elongated member adapted to be positioned to bridge the frame, theelongated member having a slot formed therein and adapted to provideaccess to the skin during the manufacturing process, the at least oneelongated member including first and second end portions adapted to besecured to substantially prevent movement of the elongated memberrelative to the frame; and a plurality of pressure applying devicesoperatively attached to the at least one elongated member and disposedtherealong, each pressure applying device including a contact membermoveable relative to the elongated member and adapted to engage thesurface of the work piece, and a resilient member operatively coupled tothe contact member and to the elongated member, the resilient memberbiasing the contact member away from the elongated member to apply aclamping force to the skin holding, the skin against the frame duringthe manufacturing process.
 34. The apparatus of claim 33 wherein theresilient member includes a spring.
 35. The apparatus of claim 33wherein the resilient member includes a resilient material.
 36. Theapparatus of claim 33, wherein at least one of the plurality of pressureapplying devices applies at least one of a hydraulic pressure and apneumatic pressure.
 37. The apparatus of claim 33, wherein the at leastone elongated member includes first and second elongated portions. 38.The apparatus of claim 37, wherein the first and second elongatedportions comprises non-parallel elongated portions.
 39. The apparatus ofclaim 38, wherein the first and second elongated portions comprise acruciform shape.